Researchers are continually investigating the usefulness of various materials in the construction of actuator devices. Such devices have a multitude of uses commonly known and understood by those skilled in the art. Actuators are capable of changing form or shape in response to a stimulus or condition and, thus, to effect or "actuate" a transformation or action. Examples of actuator applications include their use as sensors for the electronic, medical, and chemical industries. In this context, the sensors are capable of reacting to changes in the environment in which they are placed and relaying a signal to indicate such a change.
Recent advances in this field relate to use of polymers as a constituent of actuator devices. Of particular interest are those polymeric systems that operate in either an electromechanical, chemomechanical, or mechanoelectrical mode, or in all such modes.
Conductive polymers such as polyaniline, polypyrrole, and polyacetylene can increase their electrical conductivity from the insulator to metallic regime upon the occurrence of certain chemical or electrochemical doping reactions. These reactions have been shown to be accompanied by a change in the volume of the polymer, such that the polymers can be manipulated to expand or contract.
Certain conductive polymer systems have been proposed as possible artificial muscles. It has been shown by Otero et al., Intrinsically Conducting Polymers: An Emerging Technology (M. Aldissi, ed.), 179-190 (1993), that a polypyrrole film can be used as an electrode in an electrochemical cell in connection with a platinum counterelectrode and a LiClO.sub.4 aqueous electrolyte solution. Movement in the polypyrrole film can be initiated by creating a potential between the two electrodes. Another polymeric system, weakly cross-linked poly(2-acrylamido-2-methyl propane) sulphonic acid (PAMPS), has been used as a possible artificial muscle material as shown by Osada et al., Nature, 355, 242-244 (1992). However, these require counterelectrodes external to the actuator device for use thus limiting their efficiency and utility.
A need exists for advanced polymeric actuator devices. Particularly, it is desired to produce polymeric actuators that operate without the need for a counterelectrode that does not participate in the actuation.